When a conventional golf club head is swung at an ordinary kinetic speed, an air flow boundary layer is produced on the outer surface of the head within a region between a face side and a back side of the head. The air flow boundary layer is exfoliated from the outer surface of the head, and thus a subatmospheric pressure region is created behind the head. Therefore, a turbulent air flow or swirling air stream is produced behind the head by the subatmospheric pressure.
In this air stream condition around the head, air in front of the head is compressed and the air pressure increased, but the air pressure behind the head is reduced. Accordingly, an aerodynamic drag due to the pressure difference in front of and behind the head is imposed on the head during the swing. It is known that such a pressure drag reduces the head speed during the swing, and thus reduces a distance of flight of a ball hit by the head. It is also known that such a pressure drag has an adverse effect on the stability of movement of the head during the swing, and thus causing a ball hit by the head to be sliced or hooked. Several attempts have been made to design golf club heads having improved aerodynamic performance. For example, U.S. Pat. No. 1,226,671 (Backus) discloses a golf putter having a plurality of holes in the face of the putter. The holes allow air to flow into a cavity located in the putter and out two venting holes, one on the top of the putter and one on the bottom.
U.S. Pat. No. 4,900,029 (Sinclair) discloses an aerodynamic shape for a golf club. The shape include a vertical airfoil and a cavity for directing air flow across the top of the club.
U.S. Pat. No. 3,794,328 (Gordon) discloses a plurality of passages extending from the face of a golf club to the rear of the club.
U.S. Pat. No. 4,444,392 (Duclos) discloses a club having an internal cavity which allows air to escape via a slot on the trailing edge of the club.
U.S. Pat. No. 4,809,982 (Kobayashi) discloses a golf club head having an air passage form the leading edge to the trailing edge of the golf club. This passage is at an angle to the base of the club.
U.S. Pat. No. 4,850,593 (Nelson) discloses an aerodynamic head having a sculptured top and a v shaped groove at the base of club head.
In an attempt to reduce the likelihood of slicing or hooking a golf ball, perimeter weighting has been provided in golf club heads. For example, U.S. Pat. No. 4,867,458 (Sumikawa et al.) discloses the use of screws as perimeter weights for a golf club.
U.S. Pat. No. 5,050,879 (Sun et al.) discloses the use of metal inserts for changing the weight characteristics of a golf club.